1. Field of the Invention
The present invention relates to an information processing apparatus such as a personal computer (hereinafter referred to as PC) having an illegal access prevention function and an illegal access prevention method for the information processing apparatus.
2. Description of the Related Art
In recent years, portable information processing apparatuses such as notebook PCs have been widely spread to the public and people can easily carry the information processing apparatuses outside. On the other hand, a large number of incidents such as the theft of the information processing apparatuses and the leakage of information recorded in the information processing apparatuses occur. This is considered a social problem. It is known that, to tackle such a problem, in general, recent PCs are added with an illegal access prevention function (also referred to as security function).
For example, in order to prevent an illegal access to a PC, a user is requested to input a password in starting the PC. When an inputted password does not coincide with a password registered in advance, an operating system (hereinafter referred to as OS) does not start and rejects start of the PC itself. In addition, when the user accesses individual information, the operating system judges whether a password is right. However, since the password consists of alphanumeric characters or signs of fixed digits, if passwords are repeatedly inputted while changing alphanumeric characters, a password could coincide with a correct password sooner or later. Therefore, it is likely that a password is decoded even if a password judgment function is simply provided. It could be difficult to effectively prevent an illegal access to individual information.
FIG. 6 is a flowchart of an operation of a conventional illegal access prevention system for a computer disclosed in Japanese Patent Unexamined Publication No. 2001-27911. A constitution of the conventional illegal access prevention system is not shown in a figure.
First, a user turns on a power supply of a PC (S601). Before starting an OS, a password confirmation processing unit of the PC causes a display device to display a password input screen and urges the user to input a password (S602). The user inputs a password from a keyboard serving as an input/output device. If the user inputs the password from the keyboard in response to the input request, the password confirmation processing unit compares the password inputted with a password set in advance (S603). When the inputted password is illegal (No in S603), the password confirmation processing unit displays a warning message on the display device (S604) and counts up a counter for counting the number of times of display of the warning message.
If the number of times of display of the warning message is equal to or less than two times, the password confirmation processing unit returns the processing to S602 (S606) and urges the user to input a password again. Alternatively, when the inputted password is a third illegal password inputted from the keyboard in S606, the password confirmation processing unit turns off the power supply of the PC (S607). When the password inputted in S603 coincides with the password set in advance (Yes in S603), the password confirmation processing unit starts the OS and permits an access to the PC (S605).
As explained above, it is possible to prevent an illegal access to the computer, which the OS cannot prevent, at a stage of power supply to the PC. This makes it possible to use the OS in safety without concern about copy or deletion of a file by an illegal user. In a state in which a medium, for example, a hard disk drive (hereinafter referred to as HDD) having data recorded therein is mounted on an apparatus such as a PC, once a password is set on this PC, a power supply is turned off when input of a password is tried a plural times unless the correct password is inputted. As a result, it is certainly difficult to read out a content in the medium.
In a constitution disclosed in Japanese Patent Unexamined Publication No. H11-259369, passwords are compared when an information processing apparatus is started. When it is judged that a trial for an illegal access such as input of a wrong password is performed, a program in a flash memory such as a Basic Input/Output System (hereinafter referred to as BIOS) is rewritten. Consequently, a value as the information processing apparatus is reduced and a content of a secondary storage device such as an HDD is destroyed to prevent the leakage of information. When a correct password is not inputted within a predetermined number of times of input, a program and data desired to be read out are erased by a mainframe such as a PC. This is stronger against an illegal access.
In a constitution disclosed in Japanese Patent Unexamined Publication No. 2000-78127, as an illegal writing prevention method of preventing illegal writing in an individual information area of a memory built in a radio selective calling receiver, a password for allowing an access to the individual information area is stored in the memory. Coincidence/non-coincidence of an inputted password and a stored password is judged and the number of times of non-coincidence is counted by a counter. When the number of times of non-coincidence exceeds a predetermined value, information in a predetermined portion of the memory is erased to make it impossible to write information in the individual information area after that. When a correct password is not inputted within a predetermined number of times, a program and data desired to be read out are erased by a mainframe such as a PC. This is strong against an illegal access as in the example described above.
However, in the constitution disclosed in Japanese Patent Unexamined Publication No. 2001-27911, although the power supply is turned off when input of a password is tried a plural time, it is possible to decode a password through trial of a finite number of times. When the password is decoded, it is still possible to illegally read out data recorded in the HDD with a method of, for example, starting the OS from another device when the PC is started.
In the constitution disclosed in Japanese Patent Unexamined Publication No. H11-259369, even if erasure of the HDD is started, it is possible to illegally readout data recorded in the HDD with a method of, for example, forcibly turning off the power supply of the PC and subsequently decoding a password with the same method as described above or taking out the HDD and connecting the HDD to another PC. Similarly, in Japanese Patent Unexamined Publication No. 2000-78127, it is possible to illegally read out data recorded in the HDD with a method of, for example, taking out the HDD and connecting the HDD to another PC.